PROJECT SUMMARY/ABSTRACT DESCRIPTION: See instructions. This must contain a summary of the proposed activity suitable for dissemination to the public (no proprietary/confidential information). It should be a self-contained description of the project and contain a statement of objectives and methods to be employed. It should be informative to other persons working in the same or related fields. DO NOT EXCEED THE SPACE PROVIDED. The goal of the proposed research is to discover biologically important genetic variants underlying risk for heroin addiction. We will use existing data to map biological pathways and genetic variants' effects, such as effects on gene regulation (DNA methylation and mRNA expression) and protein function in human brain tissue. We will apply this knowledge to conduct pathway-based genome-wide association study and the first function-weighted GWAS analyses of heroin addiction using the largest sample size, by far, for this phenotype to date (total N=52,362 for discovery and N=24,205 for independent replication). The chronic, remitting/relapsing brain disease of addiction affects millions of US citizens and costs billions of dollars per year. The prevalence of heroin addiction and its public health consequences are growing (e.g., increasing overdose deaths for 14 years running). Heritability of heroin addiction is substantial (~60%). However, after more than 30 years of research, including four standard GWAS analyses and many linkage and candidate gene studies, few specific genetic variants have been conclusively identified for this disease. Successful GWAS and other gene-mapping studies for complex diseases highlight three critical factors: (1) the vast majority of reproducibly associated genetic variants are functional, either coding variants that tissue specific; and (3) sample sizes ?10,000 are often necessary. encode protein changes or noncoding variants that may exert regulatory effects; (2) gene regulation is highly Our proposal capitalizes on these facts in a novel approach to gene discovery for addiction across three aims. ? Specific Aim 1: Conduct pathway-based GWAS analyses of heroin addiction (N=52,362) and test for independent replication (N=24,205). ? Specific Aim 2: Integrate available and new information on putative variant function in human brain and optimize fwGWAS methods. ? Specific Aim 3: Conduct function-weighted GWAS analyses of heroin addiction and test for independent replication. Our pathway-based GWAS and function-weighted GWAS approaches will greatly improve the likelihood of meaningful discovery over standard GWAS through informed analyses based on known gene pathways and genetic variants' biological relevance specifically in the brain, while retaining a genome-wide scope. The logic of our approach is straightforward yet innovative, shining the brightest light on biologically relevant variants to uncover new gene regions underlying heroin addiction.